Conventionally, a piezoelectrically driven valve and a piezoelectrically driven flow rate control device of this type are widely known (for example, see Japanese Patent No. 4119109 and Japanese Patent No. 4113425, etc.).
An example of a piezoelectrically driven flow rate control device, including a conventional piezoelectrically driven valve, is described hereinafter by referring to FIG. 2 to FIG. 6. In FIG. 2, the reference numeral 1 denotes a valve main body, the reference numeral 1a denotes a hole portion provided in the valve main body, the reference numeral 2 denotes a metal diaphragm valve element, the reference numeral 3 denotes a diaphragm presser, the reference numeral 4 denotes a presser adapter, the reference numeral 8a denotes a ball, the reference numeral 9 denotes a lower portion bearer, the reference numeral 10 denotes a piezoelectric actuator, the reference numeral 11 denotes an upper portion bearer, the reference numeral 12 denotes a positioning cap nut, the reference numeral 13 denotes a lock nut, the reference numeral 14 denotes a protective case, the reference numeral 15 denotes a connector, and the reference numeral 18 denotes an elastic member including stacked disc springs, the reference numeral 23 denotes a piezoelectric actuator support cylinder, the reference numeral 24 denotes a cylinder fixing/guide body, the reference numeral 25 denotes an O-ring, the reference numeral 26 denotes a split base, the reference numeral 27 denotes an attaching bolt, and the reference numeral 28 denotes a bearing.
In the example shown in FIG. 2, between the lower portion bearer 9 and the piezoelectric actuator 10, the ball 8a formed separately is interposed. However, it is also possible that a protrusion having a spherical tip end is formed integrally at the center of the lower end face of the piezoelectric actuator 10, and is used as the ball 8a and brought into contact with the lower portion bearer 9.
The valve main body 1 is made of stainless steel, and includes a hole portion 1a forming a part of a valve chamber, and a fluid inlet, a fluid outlet, a fluid passage, a valve chamber, and a valve seat, etc. The metal diaphragm valve element 2 is formed of a thin plate made of nickel-chromium alloy steel, and has an upturned dish shape whose central portion slightly swells upward. The metal diaphragm valve element 2 may have a tabular shape, and may be made of stainless steel, Inconel alloy, or other alloy steels. Furthermore, the metal diaphragm valve element 2 may use one diaphragm, or use layers of two or three diaphragms.
The metal diaphragm valve element 2 is disposed inside the valve chamber so as to be opposed to the valve seat, and by tightening the attaching bolt 27 into the valve main body 1 via the presser adapter 4, the split base 26, and the cylinder fixing/guide body 24, and the outer peripheral edge of the metal diaphragm valve element 2 are held and fixed airtightly to the valve main body 1 side. The presser adapter 4, the cylinder fixing/guide body 24, and the split base 26, etc., are made of metal such as stainless steel.
The piezoelectric actuator support cylinder 23 of the piezoelectric actuator (piezostack) 10 is formed into a cylindrical shape from Invar material with a small thermal expansion coefficient, and as shown in FIG. 3 and FIG. 4, an upper portion thereof is formed into a large-diameter portion 23c that houses the piezoelectric actuator 10, and a lower portion that is formed into a cylindrical reduced-diameter portion 23d that is reduced in diameter and houses the lower portion bearer 9 and the elastic member 18, etc. At the lowest end portion of the support cylinder 23, a cavity portion 23e in which the diaphragm presser 3 is fitted is formed, and here, the diaphragm presser 3 is inserted and fixed as shown in FIG. 2.
FIG. 3 is a longitudinal sectional view of the piezoelectric actuator support cylinder 23, and FIG. 4 is a sectional view taken along line I-I in FIG. 3. Near the boundary between the large-diameter portion 23c and the reduced-diameter portion 23d of the piezoelectric actuator support cylinder 23, a hole portion 23a, in which split base pieces 26a shown in FIG. 5 are inserted and combined from both sides so as to be opposed to each other, is formed by cutting both side portions of the outer wall portion to a fixed depth by a fixed length. Specifically, from both sides of the hole portion 23a, the split base pieces 26a that are half-split of the split base 26 (described later in more detail) are fitted so as to be opposed to each other, and integrally held and fixed as the split base 26 by the cylinder fixing/guide body 24. Before fitting the split base pieces 26a, the elastic member 18 is inserted and fitted to the bottom portion 23b of the reduced-diameter portion 23d as shown in FIG. 2.
FIG. 5 is a plan view showing a fitting state of the conventional split base 26, and FIG. 6 is a sectional view taken along line II-II in FIG. 5. As clearly seen in FIG. 5 and FIG. 6, the two split base pieces 26a are formed by half-splitting a short cylindrical body at the center portion, the short cylindrical body having an upper wall 26b and having a flange portion 26c formed on the lower end outer periphery and an insertion hole 26d and a fitting portion 26e formed on the upper wall 26b, and by fitting the split base pieces 26a to each other so as to be opposed to each other, the split base 26 is formed.
Specifically, as shown in FIG. 2 and FIG. 6, the flange portion 26c is subjected to a pressing force from the lower end of the cylinder fixing/guide body 24 and acts to press the presser adapter 4, and the insertion hole 26d allows the wall body of the reduced-diameter portion 23d of the piezoelectric actuator support cylinder 23 to be inserted through, and further, the fitting portion 26e is positioned between the lower portion bearer 9 and the wall body of the support cylinder 23 and acts to position the three members 9, 23, and 26.
The bearing 28 is formed of a bearing receiver 28a and small balls 28b, and is disposed above the upper portion bearer 11 and makes smooth turning of the positioning cap nut 12.
A control valve shown in FIG. 2 is mainly used as a control valve for a pressure type flow rate control device, so that, as shown in FIG. 2, the valve main body 1 is provided with an orifice mounting portion 30 including an orifice guide 30a, a gasket 30b, and an orifice 30c, etc., a pressure sensor mounting portion 31 including a pressure sensor 31a, a gasket 31b, a connector 31c, a presser flange 31d, and a fixing bolt 31e, etc., and a primary connecting portion 29 including a connection guide 29a and a gasket 29b, etc. The reference numeral 32 denotes a control circuit mounting plate for a piezoelectric actuator, etc., provided inside the protective case 14.
The pressure type flow rate control device, as a basic principle, adjusts an orifice upstream side pressure P1 by a control valve on the orifice upstream side in a state where the pressure P1 is kept approximately twice or more as high as the downstream side pressure P2, thereby controlling a flow rate Qc on the orifice downstream side to a set value by calculating Qc=KP1 (K=a constant), and is disclosed in Japanese Published Unexamined Patent Application No. H08-338546, etc.
To assemble the control valve, the metal diaphragm valve element 2, the presser adapter 4, the piezoelectric actuator support cylinder 23 to which the diaphragm presser 3 is fixed, the elastic member 18, the split base 26, and the lower portion bearer 9 are fitted in order into the hole portion 1a of the valve main body 1, and the piezoelectric actuator support cylinder 23 is inserted and fitted into the valve main body 1 via the cylinder fixing/guide body 24. Next, the ball 8a, the piezoelectric actuator 10, the upper portion bearer 11, and the bearing 28 are inserted and fitted in order into the piezoelectric actuator support cylinder 23, and an actuation stroke of the metal diaphragm valve element 2 by the piezoelectric actuator 10 is finely adjusted to a set value by adjusting the tightening amount of the positioning cap nut 12 forming a positioning member.
By tightening and fixing the cylinder fixing/guide body 24, as described above, the split base 26, the support cylinder 23, the lower portion bearer 9, the elastic member 18, the diaphragm presser 3, and the diaphragm valve element 2, etc., are automatically fixed to predetermined positions in an orderly manner, and by tightening the positioning member 12, the central axes of the ball 8a, the piezoelectric actuator 10, and the support cylinder 23, etc., are highly accurately aligned.
Referring to FIG. 2, when a valve opening signal is input (input voltage: 0 to 120V) from a control circuit (not illustrated) via the connector 15, the piezoelectric actuator 10 extends by a set value (e.g., 0 to 45 μm). Accordingly, a pushing-up force of approximately 40 to 80 kgf is applied to the piezoelectric actuator support cylinder 23, and the piezoelectric actuator support cylinder 23 moves up by the set value against an elastic force of the elastic member 18 while the central axis is held by the O-ring 25 of the cylinder fixing/guide body 24. As a result, the diaphragm valve element 2 separates from the valve seat due to the elastic force, thereby opening the valve.
On the contrary, when the valve opening input is turned off, the piezoelectric actuator 10 restores to the original length, and as a result, the bottom portion of the piezoelectric actuator support cylinder 23 is pushed down by the elastic force of the elastic member 18 and the metal diaphragm valve element 2 is seated on the valve seat by the diaphragm presser 3, thereby closing the valve.
When the valve opening stroke is 45 μm and the opening diameter of the valve seat is 1 mmφ, an actuation time required for fully opening the valve from the fully-closed state is approximately 30 msec or less.